A few questions on flood and drain systems.

How often should a grow bed, flood/drain? I know I read in the book it says with timer systems it should be timed on for 15 minutes every hour. But what are the specifications for a flood and drain?

Also, I have 8" of 'wet zone' in the bottom of my grow bed along with 2" of 'dry zone' on top that does not get flooded. How do I start growing plants from seeds now? I have 2" rockwool plant starter cubes and I was thinking to position them just so the base gets touched by the water at peak flood? Or should I keep them in the complete dry zone and water them each day until their roots reach the peak of the flood in the grow bed? Or can I just leave them in the dry zone and have it all work on its own?

And one last thing, where should I place the hose that pumps water into the grow bed? Should I put it below the 'dry zone' so it keeps that zone, dry? Or should I attach it to a sprinkler like system at the top to get all the plants wet? This makes me wonder though how the top zone could be considered dry if water is constantly being poured over top 24/7.

Thanks in advance, I am almost done with my system and I think so far it is looking fantastic! It is a miniature, 20 gallon growbed, 10 gallon tank, and 14 gallon sump. I will soon be putting up pictures and videos when I get it functioning.

Replies to This Discussion

15 minutes complete flood and then drain cycles are good enough. As long as seeds get sufficient moisture and are not soaking wet they sprout easily. The inflow should be at the opposite end to the outflow. This can be positioned above or below the dry zone. If you place above the dry zone only that localized area, and not the entire dry zone will become wet. If the pipes are above the media they allow for easier inspection/cleaning to easily recognize/correct any problems which may arise.

Often, I scratch away some of the surface media, then sprinkle some seeds. Most spots tend to germinate and grow but sometimes I repeat some of the planting. I use short pieces of PVC to plant the seeds into, then remove the pipe after the plants are growing - this is just to help with spacing and to keep the media from covering the seeds up too much - too it helps you to know what sprouted, what didn't and what you need to replant

If you pump directly to the surface of your media, you can more easily observe whether or not the pump is actually pumping.

Flood and drain cycles vary widely. If you have other sources of aeration, then possibly you can flood less often, depending on stocking. I've found that lots of aeration is a good thing.

I'll defer to harold, but I don't think his pumps turn on and off, but I could be very wrong. I have a hose bib connected to the pump that feeds my plant beds, so when I direct seed, I just sprinkle the seeds every night until their roots take hold. pre-growing in various forms of starter media will get your roots into the flood zone. I would recommend reading about the kratky method for plant growth as I suspect the science behind his research is what drives us in flood and drain. I can also tell you I've planted my AOK plugs into my media above the flood level and it didn't take long for the roots to find their way into the flood zone.

Alex, I think you are confusing flood and drain cycles with inflow. You can use a constant flow pump putting a stream of water into your growbeds continuously.. But by using a bell siphon, the bed will drain intermittently, so actually it is flooding and draining cyclically..

Other Alex, your system should flood and drain once every 15-20 minutes approx. You should not use a sprinkler to distribute your water. The vast majority of plants actually do not like to get wet. They only want water at the roots. Like Harold said, inflow should be on the opposite side of your outflow, that way everything gets distributed from one side of the growbed to the other. You can put it above or below your media. If you keep it above, your water will fall at a greater height, resulting in slightly more oxygen and you'll be able to observe right off the bat if your pump is running or not. If you keep it below, you will end up with a little less algae on the surface of your growbed (usually in a concentrated area where the water pours in).

Feel free to take a look quick look some of the pictures on my page. You should be able to see how my plumbing is set up.

Alex said:

So it's bad to flood/drain all day and night 24/7? 15 minutes every hour is what I am to aim for?

Thanks for all the great responses! I have definitely learned a thing or two from what has been shared with me. Right now I am going to keep my pump hose under my dry zone.

As well I just put some seeds in the system, didn't use the rockwool but instead just dropped them a layer or two below the hydroton. I'll be watering them each day with a little fish water until I see a strong sign of sprouts that seem to be digging their way into the wet zone.

As for how often my system floods and drains, it's a slow flood fast drain. It takes 5 minutes to flood completely and drains in approximately 30 seconds. This cycles my tank about %80 in one cycle so every hour my fish tank is cycled about 8.8 times and the growbed floods 11 times. I think these seem like some pretty promising results so right now I will be monitoring ph, ammonia, nitrite, and nitrate levels in my spare time until the plants take off!

Wow that's a high turnover rate. The minimum recommended turnover of the FT is at least once per hour in a passive AP system. By passive, I mean without added aeration. At 8.8 times/hour you're very high. Some plants likes dry periods between fill/drain time more than others, so if you're finding yourself with struggling plants or soggy roots and you need to reduce the turnover rate, without reducing the pump size, you can incorporate a bypass line from the pump directly into the FT. With this you can adjust exactly how much water goes to the Gb's, and by extension your fill/drain timing. To add a bypass line, simply tap the pump to Gb pipe and plumb this directly into the FT with a valve at the end.